CS50 Pset4 Recover

Question

I had been working on this for 6+ hours and could not figure out what was going on. All 50 images are produced, but when I opened them, I saw no pictures in it. What is wrong? Please help me out, and thank you so much!!!!! Here are the codes:

/**
 * recover.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Recovers JPEGs from a forensic image.
 */

#include <stdio.h>
#include <stdint.h>

int main(void)
{
    // open CF card 
    FILE* CF_card = fopen("card.raw", "r");
    if (CF_card == NULL)
    {
        printf("Could not open %s.\n", "card.raw");
        return 1;
    }

    // define a counter that counts the number of JPEGs found, a buffer, a character that denotes a filename, and a global variable for the output file
    int JPEG_counter = 0;
    uint8_t buffer[512];
    char filename[8];
    FILE* img = NULL;

    // read CF card
    while(fread(&buffer, sizeof(buffer), 1, CF_card) == 1)
    {

        // JPEG signature hunt
        if((buffer[0] = 0xff) && (buffer[1] == 0xd8) && (buffer[2] == 0xff) && (buffer[3] >= 0xe0) && (buffer[3] <= 0xef))
        {
            if (img != NULL)
            {
                fclose(img);
            }

            // JPEG found, create new file
            sprintf(filename, "%.3d.jpg", JPEG_counter);

            // open newly created file
            img = fopen(filename, "w");
            if (img == NULL)
            {
                fclose(CF_card);
                fprintf(stderr, "Could not create %s.\n", filename);
                return 2;
            }

            // keep track of JPEG found
            JPEG_counter++;

            // write to newly created file
            fwrite(&buffer, 512, 1, img);
        }

        // continue to write to the same file until the next JPEG is found
        else if (JPEG_counter > 0)
        {
             fwrite(buffer, sizeof(buffer), 1, img);
        }

    }
    // close the file
    fclose(CF_card);
    return 0;
}

Answer 1

Well, it took me a while to recognize the root cause. Along the way, I verified that output files were the right size, that the opening 120 bytes were right, etc., etc.

Then, I noticed that the first byte of the second and every block that followed was always ff. Hmmm.....

Since it took so long for me to find it, I'll narrow the search for you. ;-) Look at the following line:

    // JPEG signature hunt
    if((buffer[0] = 0xff) && (buffer[1] == 0xd8) && (buffer[2] == 0xff) &&
       (buffer[3] >= 0xe0) && (buffer[3] <= 0xef))

Do you see anything wrong??? There's an error. To teach the lesson, and make sure it burns into the farthest reaches of your brain, (and payback :-P ) I'll let you find it yourself! :-D I will guarantee that the problem lies in this line of code though.

(I want this to set in because I made this mistake over and over when I first started programming and it haunted me for a long time. Hopefully, this will save you from that. )

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)